1. Field of the Invention
The present invention relates to a waste heat recovery system for a liquid-cooled internal combustion engine, in which engine heat that is absorbed by engine cooling liquid in a water jacket and exhaust gas heat that is absorbed by the engine cooling liquid in a first heat exchanger for heat absorption from exhaust gas (a gas/liquid heat exchanger) is recovered from the engine cooling liquid by heat transfer from a second heat exchanger for heat recovery (a liquid/liquid heat exchanger).
A conventional waste heat recovery system for a liquid-cooled internal combustion engine, for such a purpose is one disclosed in U.S. Pat. No. 4,226,214.
The conventional system is provided with a circuit for a waste heat recovery from an engine, and is composed of a first heat exchanger for heat absorption from exhaust gas and a second heat exchanger for heat recovery, both heat exchanges being connected in series to a water jacket within an engine body, and in which the engine cooling liquid in the water jacket is adapted to be returned to the water jacket through the first heat exchanger and then the second heat exchanger. Therefore, the engine cooling liquid which absorbs the heat in the water jacket also absorbs the exhaust gas heat during flow through the first heat exchanger to reach a high temperature and then radiates the heat contained therein to an external thermal load such a hot-water reservoir or the like through the second heat exchanger.
There are, however, the following disadvantages associated with the above-mentioned prior art.
In the case that the output of an internal combustion engine is taken out as electric power or the like during continuous operation, when the heat transfer is stopped by the stoppage of the operation of the external thermal load or when the heat quantity radiated in the second heat exchanger gets less than that absorbed in the first heat exchanger due to a reduction of the heat quantity consumed in the external thermal load, the temperature of the engine cooling liquid gets increase excessively because the heat quantity transferred from the engine cooling liquid in the second heat exchanger decreases. Resultantly, the continuous operation of the internal combustion engine is hindered by its overheat and disadvantageously it becomes impossible to continue the takeout of its output power.